Functions of capillary pressure and dissolution in the CO2-flooding process in low-permeability reservoirs

Abstract

CO2 flooding has become one of most effective methods to improve oil recovery in low-permeability reservoirs. Thus, influencing factors have been specifically analyzed for their impact on oil displacement. Factors that are difficult to observe, such as capillary pressure and CO2 dissolution, have often been neglected in specific analysis. To do so, this paper combined laboratory experimentation with numerical simulation analysis to understand the specific functions of capillary pressure and CO2 dissolution in the CO2-flooding process in low-permeability reservoirs. Based on laboratory experiments with long cores applying different CO2-flooding methods, the authors established a one-dimensional numerical simulation model for CO2 flooding. After that, the model was simulated to analyze the effects of capillary pressure and CO2 dissolution for different CO2-flooding processes. The results show that the function of capillary pressure in different CO2-flooding modes is not consistent in low-permeability reservoirs; furthermore, capillary pressure is a driving force in the process of flooding and is a resistance force in the CO2-flooding process after pressure recovery. When considering CO2 dissolution in different flooding modes, its function was shown to be inconsistent in low-permeability reservoirs compared with CO2 flooding without considering CO2 dissolution; oil recovery is reduced in the CO2-flooding process, but oil recovery increases in the CO2-flooding process after pressure recovery. Therefore, in order to promote the rational and effective development of low-permeability reservoirs, it is necessary to understand the functions of capillary pressure and CO2 dissolution clearly in the process of CO2 flooding.